Use curl -sS to silence non error output.

The logstash daily curl commands output non error messages on normal
runs. Use the -sS options to curl to silence all non error message
output.

Change-Id: I7df3abdd74f6e058cf0208cefb7639202e4f9d0e
Reviewed-on: https://review.openstack.org/27316
Reviewed-by: Anita Kuno <anita.kuno@enovance.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins